Responding to an increasing demand for better accountability of drug abuse treatment funds, the State of Illinois mandated a continuum of care model to assure that clients obtain the appropriate drug abuse treatment for their specific level of need. Issued in 1995, the mandate required that as a condition of funding, providers in the public drug abuse system use a set of standardized patient placement criteria for establishing appropriate care. From a managed care perspective, the use of the continuum of care and the patient placement criteria, should provide more appropriate management of health care resources care and more effective drug treatment. This study conducts an aggregate analysis of the Illinois public drug treatment system by examining the impact of the mandates on aspects of the treatment provided and on the cost the State of Illinois plays for treatment. Using a time-series analysis to examine aggregate trends before and after the mandate and an analysis of co-variance of client-level data to control for client-mix differences across the series, we test the impact of the mandates on the Illinois drug treatment system. Data for the study are extracted from a computerized record used by the Department of Alcoholism and Substance Abuse to administer drug treatment funds. Data representing seven years of services and nearly 2,500,000 are expected to provide extremely stable parameter estimates as well as generalizability across treatment systems.